Rectangular batteries are traditionally known as the batteries in which is obtained a higher volumetric density than that of a cylindrical battery. Rectangular batteries include a flat, wound electrode structure accommodated as an electricity-generating element in a rectangular battery container. The flat, wound electrode structure is constructed by winding a band-like positive electrode plate including a non-coated positive electrode section (exposed positive electrode foil section) formed at an end portion, and a negative electrode plate including a non-coated negative electrode section (exposed negative electrode foil section) formed at an end portion. More specifically, the positive electrode plate and negative electrode plate in the wound electrode structure are wound together under a separator-insulated state to form a stack of layers so that the non-coated positive electrode section and the non-coated negative electrode section are arranged at positions opposite to each other. Even more specifically, one of the non-coated electrode sections is positioned at one side of the wound electrode structure, in an axial direction of winding, and the other non-coated electrode section is positioned at the other side of the wound electrode structure, in the axial direction of winding.
The wound electrode structure includes a positive electrode connection terminal joined to a stacked section of a positive electrode current collector that has the non-coated positive electrode section folded in layers, and a negative electrode connection terminal joined to a stacked section of a negative electrode current collector that has the non-coated negative electrode section folded in layers. The positive electrode connection terminal and the negative electrode connection terminal are connected to, for example, a positive electrode outside terminal and a negative electrode outside terminal, respectively, these outside terminals being arranged on the same surface of the battery container, such as a surface of a battery cover, on the outside of the battery container. Thus, electrical continuity is established between the positive or negative electrode connection terminal and the corresponding outside terminal. That is to say, the positive electrode connection terminal and the negative electrode connection terminal are constructed to electrically neutralize the battery container, that is, to electrically insulate the battery container from the wound electrode structure.
For the rectangular batteries of this type, a variety of measures are proposed to protect inner walls of the battery container as well as the wound electrode structure positioned inside the battery. The protection is provided by interposing an electrical insulating sheet or film between the wound electrode structure and the inner walls of the battery container. This insulating sheet or film prevents the outer-peripheral positive electrode section and negative electrode section of the wound electrode structure from short-circuiting through the inner walls of the battery container, and protects the surface of the wound electrode structure from damage when the electrode structure is inserted into the battery container.
For example, a known sheet of insulating material, as disclosed in Patent Document 1, includes one pair of wide-surface forming sections that forms one pair of wide surfaces opposed to a flat surface of a wound electrode structure, a base-forming section present between the paired wide-surface forming sections, the base-forming section forming a base opposed to that of a battery casing, and two pairs of narrow-sideface forming sections each present at one side of the paired wide-surface forming sections, the two pairs of narrow-sideface forming sections forming narrow sidefaces at both sides of a wide surface of the battery casing; wherein the narrow-sideface forming sections arranged in bag-like folded form inside the sheet are formed to be smaller than the narrow-sideface forming sections arranged outside the sheet, and thus the wound electrode structure can be easily inserted into an outer casing of the battery.